The present invention relates to a wood preservative which contains water, a copper or zinc complex dissolved in water, and an acid which fixes copper or zinc to wood.
Previously known are wood preservatives which contain a metal, usually copper or zinc, which forms amine complexes, and ammonia and carbonic acid. Such a wood preservative solution can be prepared, for example, by allowing ammonia to react with copper carbonate, whereafter the solution thus obtained is stabilized by means of ammonium bicarbonate and, when necessary, by means of carbonic acid.
Thus there are previously known as wood preservatives various compositions based on, for example, copper or zinc. Copper can thus also be fixed to wood in ways other than by precipitating it in the form of carbonate. The so-called CCA salts were developed in the 1930s, and they have since been used generally for protecting wood from decay. Such CCA salts contain copper, chromium and arsenic. Copper is used because of its fungicidal action, whereas arsenic is used mainly in order to produce an insecticidal action. Chromium is used for fixing the copper to the wood. CCA salts provide good protection against decay, but they are an environmental hazard.
One disadvantage of these previously known wood preservatives is that they do not give the wood sufficient dimensional stability. Attempts have been made to eliminate this disadvantage by using water insoluble wood preservatives which, for impregnation, are dissolved in some organic solvent. The penetration of organic solutions such as these into wood is not, however, as good as that of aqueous solutions. Furthermore, organic solvents increase the price of the wood preservative and make it highly flammable. The amount of the organic solvent can be reduced by using micro-emulsions, but such a micro-emulsion is, nevertheless, considerably more expensive than an aqueous solution.
The object of the present invention is thus to provide a water-based wood preservative which is inexpensive, non-toxic and with a high penetration into wood, which is not easily rinsed off from wood and which decreases the absorption of water into the wood.
The object of the present invention is additionally to provide a wood preservative in which the action of copper and zinc is more effective than previously.
Preservatives according to the invention can also be used as fungicides in paints, surface treatment agents, and plant pots.